Registration detection system



May 8, 1962 c. FROMMER 3,033,109

REGISTRATION DETECTION SYSTEM Filed Dec. 8, 1958 2 Sheets-Sheet 1 -MOVEME'NT MOVEMENT YELLOW YELLOW YELLOW YELLOW YELLOW kED gm b 12 RED RED YELLOW a a q 23 25 254 23 29 33 (9/ 6i? lf Ll? T/ME I M ii r//|4 A B C M CQQMWJ May 8, 1962 J. c. FROMMER REGISTRATION DETECTION SYSTEM 2 SheetsSheet 2 Filed Dec. 8, 1958 United States Patent Ufifice 3,633,109 Patented May 8, 1962 3,033,169 REGISTRATIGN DETECTIQN SYSTEM Joseph C. Frommer, Teahwood, Ghio, assignor to Hurletron Incorporated, Danville, Ill., a corporation of Delaware Filed Dec. 8, 1958, S81. No. 778,660 15 Ciaims. (Cl. 101-431) This invention relates generally to registration control and more particularly is concerned with the control of the registration of two operations performed consecutively upon a moving web, such as, for example, the continuous moving paper Web of a high speed multiple-color printing press. As will be seen, the invention is applicable as well to a device or system in which an indication is given of the condition of register, leaving the correcting to be done by other means, if at all. The word detection will be used to include both indication and control.

As will become apparent, the invention is not limited to the specific application in printing presses, although the description herein will be made with reference to such a press. For example, Where two consecutive mechanical functions performed on a moving web, of metal or the like, are capable of being identified as to their relative locations by marks of diilerent color applied simulta neously with the respective functions, the invention enables registration of such functions to be effected, or, if desired, the condition of registration of the functions to be indicated.

In the case of high speed multi-color printing presses, it is a relatively simple matter to provide a special mark on each printing cylinder, and to have the marks arranged to coincide for perfect registration. Obviously, each mar will be printed in the color of the ink which is applied to the remainder of the cylinder carrying the markprinting medium. Colored printed matter is often provided with a cross or hairline of color on each impression so that there is a superpositioning of crosses of all the colors to assist in the visual inspection of registration. This invention may operate on the basis of the use of such crosses. The edge of actual printed matter could be used, in place of crosses or special marks.

The invention herein is an improvement over the structure described and claimed in US. Patent 2,840,370 issued June 24, 1958 to Carl M. Noble, and assigned to the assignee of this application. In that patent, several advantageous structures are described, whose purposes are, among others, to eliminate the need for electromagnetic pulsing devices operated in mechanical synchronism with one of the printing cylinders, to decrease the amount of printed area required for the indicia or registration control marks, and to provide a control system which corrects for errors in registration, both as to amount and direction.

The invention herein has achieved these objects as Well, but in addition has several objects which are not characteristic of the said Noble patent. In addition, several of the disadvantages of the Noble patented structure are eliminated. These will become apparent in a discussion which follows, in which the present structure will be analyzed in comparison with that of the Noble patented structure.

The signal produced by the scanner of the Noble structure is not as ideally represented in the patent, that is, substantially perfect square waves, but has finite slope. Since the amplifier or comparison device is required to discriminate upon the basis of the amplitude of the leading or trailing edge of the signals from the scanner and this is not sharply defined, the amplifier must have high sensitivity and selectivity. Furthermore, since the basis of control is the difference in amplitudes of the leading or trailing edge of the signal depending upon which color was scanned first, changes in physical characteristics of the circuit may seriously impair, and perhaps dispel the ability of the amplifier to discriminate between the different amplitudes. In addition, the amplifier which must be used is rather complex in its circuitry.

To detail some of the above general discussion, consider the Noble patented structure. Discrimination between the efiects of the printed colors is accomplished in the Noble device based upon the principle that the respective colors will cause different amplitudes of signal output in the same photo-responsive device, for example, a photo-electric tube. The signal outputs achieved from a given pair of colors between which it is desired to discriminate do not maintain their same relative amplitudes during runs, thereby giving improper information. Changes in light intensity due to line voltage variations, aging of the light source, dirt or ink on the optical system, and the like, change the response received from the respective colors, and may so alter the resulting signals as to make the said signals useless. Variations in circuit components can also do this.

In addition to the above, the Noble structure may not provide proper information for conditions of close register because of the length of the mark in the direction of the travel of web must be considered in comparison with the amount of misregister it is desired to detect. Before the proper signal level corresponding to a particular color has been achieved from the photo-responsive device, the portions of the mark corresponding to misregister must completely cover the scanned area.

The invention herein provides structure which is simple and foolproof and will give positive registration correction or indication. The invention describes and teaches a structure which is capable of detecting the difierences in registration irrespective of signal distortions for any reasons, is economical, and can be arranged to operate in conjunction with any of a large number of known computing or comparison devices, or indicating apparatus.

The invention herein provides a structure in which there is a separation of the colors of a pair of identical marks applied by respective printing cylinders of different color upon the web, followed by the amplification and comparison of the signals produced in photo-responsive devices by the scanning of these two colors. A portion of the composite mark formed by the two colors, such as the leading edge, the trailing edge, or the whole body in the case of the crosses or hairlines is scanned as an indication of direction and amount of departure from perfect P registration, and any suitable correction means is driven to cause the press to compensate for the difference in the location of the marks, or to indicate the amount of misregister.

Light is applied to the marks and reflected from the scanned area to at least two photo-sensitive devices, in-

stead of one as in the case of the Noble patened structure,

and the relationship between the signals is detected on the basis of their relative values instead of their absolute values. photo-electric signal to vary will usually influence the two outputs from the photo-sensitive devices in substantially the same proportion so that the proportionate relation between signals will remain substantially constant while their absolute difference may vary radically. In

any event, the larger signal will continue to remain the 1 larger and vice versa, always providing a basis for proper detection of the direction of misregister.

The means for separating the colors is usually provided in a housing which comprises the scanner, and may include, in addition to the light sources, optical system and photo-electric tubes, pie-amplifier means for thephoto-electric signals, gating, integrating, and the like Those factors mentioned above which cause the 3 circuitry. This should be kept in mind in the description which follows, which is augmented by several illustrations more or less diagrammatic in form. The illustrations show preferred embodiments of the invention, and in addition show a minimum of the circuitry which can be used in order to achieve the results of the invention. For themost part the circuitry per se is known, but therein lies some of the great advantage of the invention, since the application thereof to practical structure is greatly facilitated because familiar electronic apparatus can be used to operate upon the signals produced by the system.

To facilitate a complete understanding of the invention and all of the ramifications thereof, the same has been described in considerable detail in connection with a system for use in detecting departures from register in a multi-color high-speed printing press, and either operating upon the press to bring the impressions back into registration, or indicating the direction and the amount of misregister, although as stated above, the invention is not to be considered limited to the specific application. A preferred embodiment of the invention and several modifications thereof have been illustrated in the drawings, in which the circuitry, optical systems and the like have been illustrated diagrammatically using conventionally accepted and understood symbols for parts, elements and apparatus for carrying out the invention.

In the drawings:

FIG. 1 is a generally diagrammatic view illustrating the manner in which the registration marks or indicia are applied to the moving web by the printing cylinders, and including blocks to represent various parts of the system for achieving automatic control registration.

FIG. 2 is a chart showing the relationships between the printed marks and the signals caused thereby in the respective photo-responsive devices for conditions of (a) perfect registration, (b) first impression leading the second impression, and (c) first impression lagging the second impression.

FIG. 3 is a chart similar to that of FIG. 2 except that instead of the marks being of the nature shown in FIG. 2, they comprise the crosses or hairlines usually applied in multi-color printing to aid in visual examination of the condition of registration.

FIG. 4 is a diagrammatic representation of the system of the invention showing the elements of the scanner and the circuitry of the amplifiers to which the signals from the photo-responsive devices are applied.

FIG. 5 is a diagrammatic view of an optical system of modified form.

FIG. 6 isa diagrammatic view of still another modified form.

Reference may be had to prior patents for the general details of multi-color printing systems and registration detection, indication and control devices in order to obviate the need for repetitious details, Attention is invited, for example, to Hurley Patent 2,518,325 for description of one system which uses a mechanical signal-producing device synchronized with the rotation of one of the printing cylinders and with whose signal a sacond signal is compared, this latter signal being obtained by scanning a mark printed by the second cylinder by photo-responsive means. Reference may also be had to my Patents 2,840,371, 2,840,721 and 2,840,722 for other systems with and without signal-producing devices mechanically synchronized with the rotation of a printing cylinder.

The bare essentials of a registration control system are illustrated in FIG. 1, and it may be assumed that the invention herein is embodied in that illustration. The moving web of paper is designated 10, and its direction of movement is indicated by the arrows. Two printing stations are illustrated, there being a printing cylinder 12 and its pressure or back-up roller 14 at one station for applying a yellow printed impression of the engraved or other matter carried by the cylinder 12 to the bottom surface of the web 10, and there being a printing cylinder 16 and its pressure or back-up roller 18 at the second station for applying a red printed impression of the engraved or other matter carried by the cylinder 16 to the back of the web 19. The impressions are two of as many as four or more which may eventually be applied to the web, and since all are desired to be in perfect registration, the structure which will be described may be duplicated several times along the path of the web in the press. In the later stages, the latest applied color can be compared with one of the earlier applied ones, or to the composite of some or all of them.

The printed matter is not illustrated, nor are the many other elements of a printing press shown, but it should be realized that there are idler rollers, dryers, inkers, etc. all of which are needed for the proper operation of the press, but not required to be in the view for describing the invention,

The cylinder 12 has an indicia or mark-printing area 20, which is positioned relative to the main printing area in any desired manner. If in a clear border, switches such as described in the Noble patent need not be used to disable the scanning means between the printed marks. The cylinder 16 has an indicia or mark-printing area 22 identically oriented as the area 20 so that when the printed impression from the cylinder 12 is in perfect registration with the printed impression from the cylinder 16, the printed marks caused by the printing areas 20 and 22 will be in perfect registration. The yellow mark from the area 20 is shown at 24, and that from the area 22 is shown at 26 (see FIG. 2). In FIG. 1, the printed mark 28 is a composite mark made hp of both yellow and red impressions.

The marks obviously are recurrent and are made continuously so long as the press runs. They are caused to pass a scanner, designated generally 30, which produces signals as these marks pass, and these signals are compared in the computer or comparison device 32 which provides an error signal, if any, that is applied to the correction device 34 and/or a monitor 31. The correction device may take the form of a reversible motor whose function it is to raise or lower the compensating roller 36 whereby to increase or decrease the distance subtended by the web 10 between the respective impressions of the printing cylinders 12 and 16; or it may take the form of a correction applied to the motors driving the printing cylinders, such as shown for example in Shults et al. Patent 2,151,570. The monitor device 31 may be in the form of an indicator or meter which translates the signal from the computer 32 into a movement displayed on a meter or the like.

In FIG. 2 it is presumed that the marks printed by the areas 20 and 22 are substantially rectangular and the top row of the diagrams illustrates three conditions of the composite mark printed by the areas 20 and 22. In FIG. 2A, the registration is perfect and the resulting composite mark 28 is formed of equal and coincident areas of red and yellow ink one on top of the other. For this condition, it is desired that there be no output from the computer 32 and no change in the position of the compensating roller 36. The monitor 31 should read zero. In FIG. 2B, the web 10 has been shortened by some phenomena such as shrinkage or any of a large number of reasons which are unimportant to an understanding of the invention. Thus, the yellow impression 24 arrives at the second printing station a bit too soon, and hence, it is misplaced forward of the red impression 26 by a distance such as indicated at 40. If the two areas 20 and 22 are made the same size, as preferable, the trailing edge of the resulting composite mark will be red for the same distance 40. This condition is called leading, that is, the first impression leads the second.

Under these conditions it is desired that there be pro vided an error signal operating into the correction device 34 which will lower the compensating roller 36 a slight amount decreasing the distance between the impressions 24 and 26 by the distance 40.

In the case of the lagging condition, illustrated by the upper printed marks of FIG. 2C, the red impression 26 extends to the front end of the composite mark and the yellow impression extends beyond the trailing edge by the same distance 42. The desired output signal in this case is required to raise the compensating roller 36.

In FIG. 3, instead of having substantially rectangular printed areas 24 and 26, there may be marks whose dimension along the direction of movement of the web is so small as to produce spaced marks on the web when out of register, or at least to produce marks which will result in discrete separate signals when scanned as will be described. Thus, in FIG. 3 in the top row, there are illustrated the marks resulting from the use of hairlines or crosses instead of rectangles. The first impression prints the hairline or cross 23 in yellow, and the second impression prints the hairline or cross 25 in red. The composite is designated 27. Neglecting the effect of the portion of the cross which is parallel with the movement, in FIG. 3A the yellow and red lines are in registration, in FIG. 3B the yellow line 23 leads the red line 25 by the distance 29, and in FIG. 3C the yellow line 23 lags the red line 25 by the distance 33. Note that the only condition under which all portions of the marks are superimposed is in perfect registration.

In FIG. 4 the moving web is represented by the horizontal line 10. A source of light such as an electric lamp 59 is concentrated by any suitable optical system, represented by the lens 52 to illuminate the web 10 along the track occupied by the composite marks 28 or 27 The marks, therefore, will appear in the beam of light from the light source 59 once for each revolution of the cylinders 12 and 16. Light is reflected from the web 10 through the optical system represented by the lens 54 through a suitable aperture or slot 60 and thence to the two photoelectric cells 56 and 58. So long as there are no marks on the web, the output of the cells will be constant and will not pass through the capacitors of the electrical circuit to be described. When the marks appear, the amount of light reflected to the photo-electric cells is decreased as the marks quickly pass, causing changes in the activation of the cells, and resulting in certain signals as explained below.

One of the most important features of the invention lies in the means to separate the reflections caused by the appearance of dilferent color marks in the incident beam,

from the source 50, and these means take several different forms. In FIG. 4 the light beam reflected from the composite marks is passed through the narrow aperture which may have the dimensions, say, A inch perpendicular to the direction of movement of the web, and .010 inch in the direction of movement of the web. This narrow beam of light is directed to fall upon a semi-transparent mirror 62 arranged at a suitable angle relative to the beam.

Part of the light will thus pass through the mirror 62 and may be concentrated by the optical system represented by the lens 64 to strike the sensitive plate of the photoelectric cell 56. The other part will be reflected from the mirror 62 through the optical system 66 and fall on the sensitive plate of the photo-electric cell 58.

This method of separating the reflected beam of light into two parts is exemplary, and several other structures for accomplishing this will be described hereinafter, but for the purposes of the invention, this structure may be considered broadly as means for dividing the reflected light into a least two parts, each part having the same properties as the others, irrespective of the quantitative relationship of the parts. Each of the parts is directed to effect the activation of a photo-responsive device in a manner such that the photo-responsive device discriminates between the colors which make up each part, and provides a signal which is more responsive to one color than the other. The outputs of the photo-responsive devices are then compared.

Thus, in FIG. 4, the part of reflected light which is directed to the cell 56 is passed through a color selective filter 68 which permits only the light absorbed by the yellow ink of the marks to pass, and the light which is directed to the cell 58 is likewise passed through a color selective filter 72 which permits only the light absorbed by the red ink of the marks to pass. Simple lenses of colored glass may provide the necessary color discrimination. For example, the filter 68 may be of blue glass, and the filter 72 of green glass.

Instead of using filters it is feasible to use photoelectric cells or other photo-sensitive devices which are inherently color discriminating, being more responsive or sensitive to one of the colors (light absorbed by the yellow and red ink respectively, that is, the complementary colors of red and yellow used in this example) than to the other.

Another practical structure uses a mirror 62, the transparent portion of which is selectively discriminating of color. Also the reflective coating can be so'applied as to transmit more light of one wave length than others,

reflecting more light of these other wave lengths.

FIG. 5 illustrates another structure in which the lens 54 is deliberately uncorrected for chromatic abberation whereby the two colors will focus at two difierent places spaced from one another along the axis of the lens 54. A small mirror 74 reflects the light of one color to cell 56 and another small mirror 76 reflects the light of the other color to the other cell 58. These mirrors must be extremely narrow since they must provide the effect of the aperture 60 and, in addition, the mirror 74 should not obstruct an appreciable amount of the light being transmitted to the mirror 7 6. For example, the mirror 7 4 may be drawn of glass, polished and silvered on an edge to form a front surface mirror.

In FIG. 6 there is illustrated a diagrammatic structure which is a cross section of a prism 75 having a narrow area 7 74 front-silvered and a rear area 76 back-silvered to give the same effect as the two separate mirrors 74 and 76 of FIG. 5.

The photo-responsive devices 56 and 58 produce signals which are shown in FIGS. 2 and 3, the second and The vertical ordinates represent voltage or relative signal amplitude, and the hori- Thus the conventional third rows of each figure.

zontal axis represents time. representation of wave shapes is provided.

Through suitable adjustments of the circuit constants, the signal outputs of the red (row R) and yelow (row Y) photoresponsive devices can be made of equal amplitude for the case A when the two impressions of the printing cylinders are in perfect registration one with the other. For the leading condition, as shown in B, the output from the red photo-responsive device will have a substantially lesser amplitude as at 80 and 80 for the output signal when the yellow portion of the registration mark In FIG. 2 the dimension of the marks along the direction of movement of the web is substantially greater than the dimensions of the hairlines of FIG. 3. Consequently, the composite printing of the marks 24 and 26 results usually in a figure such as 28 or those of the FIGS. 2B and 20 top row. The resulting signals are therefore formed of a continuous wave shape of varying amplitude contours. In row R for example, the signal at 23 has a first part of amplitude representing the response of the red cell to the yellow, a second part of amplitude 81 representing the response to combined yellow and red, and a third part of amplitude 83 representing the response to the red alone. The amplitude 81 is theoretically equal to the sum of the amplitudes 80 and 83. This same analysis can be applied to the other figures of FIG. 2.

As for FIG. 3, the hairlines 23 and 25 will be practically spaced apart for all conditions of misregister. Thus, there will be two closely occurring signals when the hairlines are scanned. In row R for condition B, leading, the left hand signal which is the response of the red cell to the scanning of the yellow hairline 23, is of amplitude 80', substantially less than the right hand signal of amplitude 83, this latter signal being the response of the red cell to the passage of the red hairline 25.

The same analysis of the other signals of FIG. 3 can be made.

The signals from both photo-responsive devices are applied to the grids 84 and 85 of the tube 86 whose respective plates 87 and 88 are connected through suitable dropping resistors 89 and 90 to a B+ supply. Cathodes 91 and 92 are grounded, and the grids 84 and 85 are leaked to ground through resistors 93 and 94 respectively. The outputs of the two sections of the tube 86 are applied from their respective plate circuits to the grids 96 and 97 respectively of the following tube 98 through coupling condensers 99 and 100. Bias for the grids is obtained through resistors 101 and 102 which have a common series cathode resistor 103. There is provided another resistor 104 from the bottom end of resistor 103 to ground. This will essentially suppress the in-phase (identical) portions of the signals on the two grids but will allow full amplification of the out-of-phase (opposite) components. Plates 105 and 106 are also connected to B+ through suitable dropping resistors 107 and 108.

For equal signals on the grids 96 and 97, substantially no signal will appear at the plates 105 and 106. If, on the other hand, the signals are different, such difference is amplified and opposite signals will appear at the plates 105 and 106, these signals being indicative of the amount of misregister, both as to amount and direction.

The circuit 32 may or may not include the tubes 86 and 98, which may be contained in the housing of the scanner 30. This circuit can take any of a large number of different well-known forms, such as for example, that shown in Shoults Patent 2,151,570. Consequently, it is not deemed necessary to illustrate the details thereof.

The amplifier circuit, comprising the two tubes 86 and 98 may also be modified for various purposes, such as to operate from the leading portion of the signals of FIG. 2 or the trailing edges thereof, and the like. The hairline signals are readily compared in the circuit described or modified forms thereof.

Advantageously, the photo-responsive devices could operate into a circuit such as shown in my Patent 2,517,554 which would produce outputs not related to the difference of amplitudes, but to their proportion, irrespective of amplitude. Such a system would be independent of circuit changes, aging of components, dirt and ink on the parts of the optical system, and the like.

The same principles of color separation may be used in detection and/ or correction for deviations from lateral registration, that is, misregister transverse of the direction of movement of the web. The edge of the printed copy may be scanned with a slot parallel with the movement of the web, dividing the resulting light into two or more beams or parts to detect the respective color content, and readjust the lateral position of the web according to the results obtained from a comparison of the beams. As an example of this, assume that the edge portion of printed matter contains all colors. If the scanner is adjusted so that for perfect registration, the printing covers one-half of the scanner area, the signals from the colordiscriminating photo-responsive devices will indicate which color, if any, is more to one side of the desired position than the other.

Other side correction devices can be used.

It is believed that the invention has been fully explained such as to enable those skilled in the art to fully compre- 8. bend the same, and it is desired to point out that the structure of the invention is capable of wide variation without in any way departing from the spirit or scope thereof as limited only by the appended claims.

What it is desired to secure by Letters Patent is:

1. A registration detection system for use in connection with a web moving between two stations and adapted to have an operation performed on said web at each station with the operations performed in registration, means at each station applying a registration mark simultaneously with the performance on said web with at least a portion of the marks aligned transversely of the Web, the applied marks being of different color and adapted to have a predetermined spatial relationship in a composite of said marks along the length of said Web relative to one another for the condition of registration of said operations, means illuminating said marks, means scanning said marks and comprising a pair of photo-responsive means each producing an output signal from said composite when said marks are scanned, but each photo-responsive means being sensitive in a different degree to the said colors, whereby the amplitude of the respective signals at any given instant Will depend upon the color or colors being scanned at that instant and, electronic comparison means having said signals applied thereto and providing an output related as to direction and amount with the condition of registration of said operations, considered along the line of movement of the web.

2. A system as claimed in claim 1 in which the photoresponsive means comprise photo-electric cells each having a different color discriminating characteristic.

3. A system as claimed in claim 1 in which each photoresponsive means comprises a photo-electric cell and a color discriminating filter intercepting all light entering said cell.

4. A system as claimed in claim 1 in which said scanning means includes means for separating the light reflected from said web into two different wave length parts of difierent color and directing said parts to said photoresponsive means.

5. A system as claimed in claim 4 in which said lightseparating means comprises a semi-transparent member arranged to transmit one part and reflect the other part.

6. A system asclaimed in claim 4 in which said light separating means comprises a prism having two of its faces provided with reflective areas for directing light in opposite directions.

7. A system as claimed in claim 1 in which said scanning means includes an optical system which focuses light of different colors at different points and means are provided at these points to reflect the light focused thereat to the respective photo-responsive means.

8. A register detection system for a web moving between two stations and having an operation performed at each station, and each station having means for applying a mark thereat in color simultaneously therewith and having the same location relative to the results of its respective operation, and the marks being substantially along transversely of said web, there being a different color for each mark, the spatial relation between the applied marks in their composite along the direction of the web being a measure of the registration of said operations upon said web, comprising means illuminating the web along a track parallel to the direction of movement thereof and aligned with said marks, means for separating the light reflected from said web into two parts, a pair of color-discriminating photo-responsive means each producing an output signal related to the amount and color of light applied thereto, the light parts being respectively directed to said photo-responsive means, and an electronic comparison means having said output signals both applied thereto and providing a signal output which is related to the condition of registration of said operations, at least as to direction.

9. A system as claimed in claim 8 in which said comparison means comprises at least a pair of electronic amplifiers balanced one relative to the other and providing no output when the operations are in registration, but becoming unbalanced under conditions of mis-register to provide an output signal from one or the other amplifier.

10. A system as claimed in claim 8 in which the output signals from said photo-responsive means are adjusted to be equal under conditions of registration.

11. In a registration detection system which has a moving web and registration control marks of different colors applied thereto from two stations simultaneously with respective operations performed on said web, the marks adapted to be coincident when the operations performed at the respective stations are in registration and in which means are provided for varying the timing of the operations to bring them into registration if out of register, means providing a registration control or detection signal output related to the condition of registration and comprising, a scanner having illuminating means directed to illuminate the web at the location of said marks as the marks pass, a pair of color-discriminating photoresponsive means simultaneously receiving the reflected light from the composite of the marks and each having a different color sensitivity to the respective colors, and a different sensitivity than one another, each photo-responsive means providming an output signal the amplitude of which is a function of the color or colors received thereby, and a comparison device energized by both of said output signals simultaneously for comparing said output signals and providing said first mentioned registration control or detection signal output.

12. A structure as claimed in claim 11 in which said illuminating means comprises a single source and means are provided to separate the reflected light into two parts of different color, each directed to one of said photoresponsive means.

13. A structure as claimed in claim 12 in which each photo-responsive means includes a photo-electric cell and a color fitlter before the cell.

14. In a device of the character described which includes means for continuously applying a pair of identical marks of different color to a moving web at two different stations in substantially coincident relation to provide identical composites of the marks evenly spaced along the Web; means for comparing the spatial relation between said marks to determine the degree of coincidence, if any and comprising: means illuminating the composite, means separating the reflected colors of the respective marks, photo-responsive devices arranged to receive the separate colors and provide separate output signals, the character of which is dependent upon the amount of light respectively received, and means for comparing said signals and providing a single output signal the amplitude of which is a function of the degree of coincidence.

15. In a registration detecting system of the class wherein a mark reflecting light rays of one wave-length is repeatedly applied in one location on a continuously moving web from a first station and a second mark reflecting light rays of another wave-length is repeatedly applied on said moving web at substantially said location from a second station spaced along the direction of movement of the web, whereby a composite mark reflecting light rays of said one and said other wave-length is repetively applied on said web, the improvement comprising means responsive to the light rays reflected from said composite mark for directing light of said one wavelength in one direction and light of said other wavelength in another direction, photo responsive means individually associated with each direction and responsive to the light reflected in that direction for producing an amount of electrical current individually corresponding to the particular light wave-length reflected in that direction, and means operated in accordance with the amount of current produced simultaneously by each photo responsive means for controlling the relative location along the web at which the marks are applied.

References Cited in the file of this patent UNITED STATES PATENTS 1,838,389 Goldberg Dec. 29, 1931 2,151,570 Shoults Mar. 21, 1939 2,348,862 Sorkin May 16, 1944 2,444,261 Kelling June 29, 1948 2,632,855 Bendz Mar. 24, 1953 2,764,086 Huebner Sept. 25, 1956 2,774,276 Glasser Dec. 18, 1956 2,840,370 Noble June 24, 1958 2,969,016 Crosfield et a1. Ian. 24, 1961 

